10.1.2 TimeCounter Engines

TimeCounter engines are animation engines that produce cyclic output. They start counting from some start value to some stop value, generating output while counting, and after reaching the stop value the engine starts again from the beginning. The important input fields are:

• min: the minimum (integer) value of the count.
• max: the maximum (integer) value of the count.
• step: the increment at each step (default is 1).
• frequency: The (floating-point) number of cycles of counting from min to max per second.

The important output field is:

• output: the current (integer) value of the count.

Example

Here is a complete Inventor .iv file for a simple example where the radius of the base of a cone changes in response to the output of a TimeCounter engine. Just cut and paste the text into a file named test.iv and then do ivview -q test.iv:

#Inventor V2.0 ascii

Separator {
    PerspectiveCamera {
        position        0 1 10
    }
    Cone {
        bottomRadius = 
            TimeCounter {
                min 0
                max 3
                frequency 0.2
            }
            . output
        height 2
    }
}

You should note several things about this example:

• An initial camera position is set that will make it easier to view the scene from a comfortable distance as the cone changes size.
• The bottomRadius field actually requires a floating-point number, but the output field it is connect to produces an integer value. Thankfully, in Open Inventor the integer values are quietly converted into floating point values when necessary, which is why this example works.
• The bottomRadius value will alternate between 0.0, 1.0, 2.0, and 3.0, before starting the cycle again. A cone with a bottom radius of 0.0 is no cone at all, which is why the image will disappear whenever the TimeCounter engine starts a new counting cycle.
• Setting the frequency field to 0.2 means that one complete counting cycle will take 1 cycle / 0.2 cycles-per-second = 5 seconds.